A recent investigation into undersized mud crabs has uncovered faulty crab gauges being sold in Townsville.

Minister for Primary Industries, Fisheries and Rural and Regional Queensland Tim Mulherin said gauges from a number of outlets were faulty.

"They have been found to measure below 150 mm - the minimum size limit for mud crabs," he said.

"The discovery was made as part of an investigation into the exporting of seafood.

"QBFP officers spent three days intercepting consignments of mud crabs at a depot in Townsville where two undersized mud crabs were seized.

"Further information from the commercial fisher who supplied the crabs revealed that his commercially-bought crab gauge measured less than 150mm.

"I would recommend all bait and tackle stores who stock crab gauges check the size of their stock."

Queensland Boating and Fisheries Patrol investigator Tony Loader said a number of retailers were con tacted.

"Two retailers confirmed their stock of crab gauges were also measuring less than 150 mm," he said.

"If you have purchased a faulty product you should contact the supplier to resolve the issue."